Transmission clutch control

ABSTRACT

In a hydraulic transmission, the movement of the directional valve into its neutral position automatically effects movement of a control valve to relieve the transmission forward and reverse clutches of hydraulic pressure. When the directional valve is thereafter moved to forward or reverse, hydraulic pressure is applied to one of the clutches but at a controlled rate through automatic metered movement of the control valve. The control valve may also be moved manually so as to contribute inching.

United States Patent lnventor John C. McPherson Philadelphia, Pa.

877,744 Nov. 18, 1969 Nov. 9, 1971 Eaton Yale 81 Tovvne Inc.

Cleveland, Ohio Appl. No. Filed Patented Assignee TRANSMISSION CLUTCHCONTROL 31 Claims, 5 Drawing Figs.

vs. 01 192/51, 74/010. 11,91/444,91/44s, 91/459, 91/461, 192187.191111.121. ..F16d 25/10, Fl5b1l/12,F15bl3/044 Field 01 Search 91/444,

448, 459, 461; 192/51, 87.19, 87.18; 180/53 DC; 74/DlG. l l, DIG. 2

lgjlfisi ggh [56] Relerenoes Clted UNITED STATES PATENTS 2,188,2791/1940 Hey 192/87.19 X 2,313,438 3/1943 Hoelscher. 91/448 X 2,968,9671/1961 Ross, Jr. 74/DlG. 2 3,199,647 8/1965 Staah l92/87.l9 3,220,31811/1965 McGuire 91/461 3,527,328 9/1970 Maurice l92/87.19 X FOREIGNPATENTS 900,470 7/1962 Great Britain 180/53 DC Primary Examiner-Allan D.l-lerrmann Attorney-Teagno & Toddy ABSTRACT: In a hydraulictransmission, the movement of the directional valve into its neutralposition automatically effects movement of a control valve to relievethe transmission forward and reverse clutches of hydraulic pressure.When the directional valve is thereafter moved to forward or reverse,hydraulic pressure is applied to one of the clutches but at a controlledrate through automatic metered movement of the control valve. Thecontrol valve may also be moved manually so as to contribute inching.

To nzvznsz TO FORWARD CLUTCH CLUTCH 27 29 l 26 2e L J TRANSMISSIONCLUTCH CONTROL BACKGROUND OF THE INVENTION This invention relates to ahydraulic transmission, and more particularly, to the control of theclutches of a hydraulic transmission. Those skilled in the art are awareof the fact that the swift movement of hydraulic fluid to the clutchesof a hydraulic transmission, will cause the vehicle in which thetransmission is used, to jerk forward or rearward because of the swiftengagement of the clutches. In an industrial vehicle, such movement maybe very damaging both to the vehicle, the operator, or the goods thatare being transported by the vehicle. My invention contemplates the useof means for preventing the swift movement of fluid to the forward andrearward clutches of a hydraulic transmission, in order to effect smoothacceleration and to prevent jerky and swift movement of a vehicleequipped with the transmission.

Workers in the art appreciate also that in a hydraulic transmission ofthe class described, it is highly desirable that the operator beprevented from changing the direction of the vehicle from forward toreverse or vice versa, while the vehicle is moving in a particulardirection. The art terms this form of changing the direction of a movingvehicle plugging." Plugging is a procedure that is frowned upon, asconsiderable damage may be caused by thus changing the direction of themoving vehicle. My invention contributes an antiplugging feature that isinherent in the construction that functions to prevent the swiftapplication of the hydraulic fluid to the directional clutches.

It is exceedingly important that the operator of a vehicle of the classutilizing a hydraulic transmission be able to control the forward andreverse clutches in order to permit a procedure that the art termsinching. Inching is a procedure that permits racing of the engine of avehicle, while permitting the clutches to slip so that the vehicle willmove very slowly. Such inching is exceedingly important in order to movea vehicle slowly uphill into a particular location, or to elevate aloadlifting platform through swift operation of a hydraulic pumpmechanism, operated by the same engine that drives the vehicle, while atthe same time the vehicle moves forward slowly through a slipping of theclutches. It is possible in my construction conceived for preventingswift application of the forward and reverse clutches, and also toprevent plugging, to permit inching without requiring complex additionalmeans. As a matter of fact, the inching procedure is inherent in myinvention and is obtained through the simple utilization of an inchingpedal connected to a part of the hydraulic clutch mechanism byrelatively conventional means.

PRIOR ART While all the various functions of my invention to bedescribed in this application may have been contributed individually byvarious mechanisms, so far as l know, it has never been possible,through the development of a single basic concept, to contributeinching, antiplugging, and slow metered application of hydraulic fluidto clutches utilizing a construction in which the three functions areinherent.

SUMMARY OF INVENTION As a feature of my invention I prevent the swiftapplication of fluid to the forward and reverse clutches of a hydraulicmechanism through the utilization of a control for the flow of thehydraulic fluid to the clutches, that is adapted inherently to preventswift flow of the hydraulic fluid to the clutches when the directionalvalve that determines whether or not fluid flows to the forward clutchor to the reverse clutch, is moved into a directional position from aneutral position.

As a particular feature of the invention, l utilize means for moving acontrol device, which may take the form ofa valve, into a position inwhich application of hydraulic fluid pressure to the clutches ceaseswhenever the directional valve is placed in a neutral position. In oneform of my invention this may be accomplished through connecting acontrol valve to means actuated by the vacuum generated by the engine.The movement of the directional valve thereafter into a directionalposition is effective to allow a gradual dissipation of the vacuum sothat there will be a gradual increased application of hydraulic fluidpressure to the directional clutches.

In another form of the invention, the movement of the directional valveto neutral excites an electromagnet for moving a fluid control valve towithdraw hydraulic fluid pressure flow from the clutches. Upon thebreaking of the circuit of the electromagnet, as when the directionalvalve is moved into a directional position, the control valve willgradually move slowly, as under the control of a dashpot, allow the fullapplication of hydraulic fluid pressure to the directional clutches.

It will be well appreciated, that since fluid pressure is dissipated bythe control valve whenever the directional valve is in a neutralposition, my construction is inherently antiplugging. Thus, thedirectional valve must move through neutral when it moves from onedirectional position to the other. Since, when it is in neutralposition, fluid pressure flow to the clutches cannot take placeefiectively, there must be a relieving of the clutch pressure and theclutches will become disengaged. Thereafter, fluid pressure at theclutch ".s will increase only at a graduated predetermined rate.

The inching control is also inherent except for the addition of atreadle. Thus, through moving the control valve by the treadle, thevalve is caused to function in the same manner as if moved by theelectromagnet or by the vacuum of the engine to dissipate the flow offluid pressure to the clutches. This movement of the control valve maybe accomplished when the clutches are in forward or reverse driveposition, so that the drive will be through slipping clutches, therebycontributing inching. Again, it is emphasized that this feature ispractically inherent in the basic combination of my invention.

DESCRIPTION OF DRAWINGS Referring now to the drawings:

FIG. 1 is a schematic illustration of my invention with the directionalvalve in reverse drive position, the control valve being in a positionto allow full application of a hydraulic pressure to the clutches.

FIG. 2 is a view similar to FIG. I, but showing the directional valve ina neutral position and with the control valve subjected to vacuum of theengine so as to relieve the clutches of their pressure.

FIG. 3 is a view similar to FIGS. I and 2, but showing the directionalvalve in forward position and the control valve moved by the inchingtreadle.

FIG. 4 is a section illustrating a detent mechanism for bolding thedirectional valve yieldingly in three positions, together with anelectrical control. FIG. 5 shows an electromagnet and dashpot of theelectrical control.

DESCRIPTION OF PREFERRED EMBODIMENTS In the drawings, the letter P inFIG. 1 designates a standard pump driven by an engine E having amanifold M. Engine E is the traction engine for the vehicle transmissionof my invention. The valve assembly for controlling the hydraulicclutches of the hydraulic transmission is in a body 10 connected to thepump P by means of a passage 11. The directional valve is in the form ofspool designated by numeral 12. By use of a link 13 connected at 14 tothe valve 12, and at 15 to an actuator valve 16, it becomes possible tomove the actuator valve 16 and the directional valve 12 together throughthe usual manually operated lever that is present in assemblies of theparticular class.

The actuator valve 16 slides in a valve body A and is form ed with alateral passage 17 connected to a drilled vertical opening 18 that isadapted to be placed in communication with a port 19, a port 20, and afurther port 21 in valve body A. It will be noted that in the reversedrive position of FIG. I, the opening 18 is in communication with theport 19, the port 19 being in communication with a chamber 22 thatthrough a screen 23 is in communication with the atmosphere. When theopening 18 is in communication with the port 20, it is then through apipe 25 placed in communication with the engine manifold M, so that thevacuum developed at the manifold will operate effectively through theopening 18, the passage 17, to draw vacuum through a pipe 26 leadinginto valve body A. The pipe 26 is connected also to a valve body 27 inwhich is found a ball valve 28. The valve body 27 is in turn connectedthrough a pipe 29 to a cylinder 30. Sliding in the cylinder 30, is apiston rod 31 fixed to a piston 32. One end of the cylinder 30 is formedwith an alr admitting opening 33 that is protected by a screen 34.

There is a bypass relatively to the passage formed by pipes 26 and 29.This bypass is through a pipe 35 arranged in bypass relation to thevalve body 27, as clearly shown in FIGS. l-3. A metering valve 36 isplaced in the pipe 35 and is manually controlled at hand wheel 37 inorder to control the volume of air that may flow through the pipe 35,all as will appear presently.

It will now be appreciated that when the actuator valve 16 is placedtogether with valve 12 in the reverse drive position of FIG. 1, passage17 will be placed in communication with the atmosphere through opening18, the chamber 22 and screen 23. Since the ball valve 28 prevents flowof air from the pipe 26 to the pipe 29 and to the cylinder 30, the flowof air to cylinder 30 will be through the volume control valve 36 as setby the manual device 37, the remainder of bypass pipe 35 and pipe 29.There will, therefore, be the same atmospheric pressure at both sides ofpiston 32, once flow through valve 36 is completed.

When the actuator valve 16 is in its forward position illustrated inFIG. 3, the passage 17 and opening 18 will be in communication withatmosphere through port 21, the chamber 22 and the screen 23. Again,atmospheric pressure will be established at both sides of piston 32. Inother words, the condition within the cylinder 30 will be the sameregardless of whether or not the actuator valve and the directionalvalve are in forward or reverse positions.

With the actuator valve 16 in its neutral position illustrated in FIG.2, the passage 17 and opening 18 will be in communication with the port20, so that the vacuum of the manifold of the ENgine E will be appliedat 25, as shown by the arrow 40. Ball valve 28 will be unseated by thevacuum as shown in FIG. 2, and the vacuum will be introduced by pipe 29to the cylinder 30 at the left side of the piston 32. The atmosphericpressure established through the screen 34 and the opening 33 willobviously then push the piston 32 to the left into its position in FIG.2, with results that will be set forth presently.

The valve body contains, in addition to the valve spool 12, a furthervalve spool 45. At its right-hand end, as seen in the drawings, thevalve spool 45 carries a spring disc 46, against which presses a spring47 urging the valve 45 into its extreme right position shown in FIG. 1against piston rod 31. Unless the valve 45 is moved by manual means in amanner to be set forth presently, or by the piston 32 and piston rod 31,as will also be described presently, it will be held by spring 47 in itsposition shown in FIG. 1.

Obviously, movement of the piston rod 31 from its position of FIG. I toits position of FIG. 2, will bring about movement of the valve 45 to theleft against the pressure of the spring 47. The valve spool 45 may alsobe moved to the left through the intermediary of a rod 48 connectedthereto at 49. Rod 48 has an abutment 50 whereby it may be moved throughthe intermediary of a treadle 51. The treadle 51 is normally pressedinto a stop position illustrated in FIG. I by a spring 52. Obviously,depression of treadle 51 by its rotation counterclockwise from itsposition of FIG. I on its pivot at 53, will move the rod 48 to the leftas illustrated in FIG. 3, all for a purpose to be set forth presently.

When the engine E is operated, the pump P is rotated and fluid will bedrawn from a usual sump 101 through the pump and pipe 11 into the valvebody 19. It will enter a chamber 55, and from chamber 55 it will bedirected through a passage 56 into the cylindrical chamber 60, in whichthe valve spool 45 slides. A valve 58 slides in chamber 55 and ispressed by a spring 57 toward the right as seen in FIG. I, the valve 58constituting a pressure relief valve which is movable to the left fromits position of FIG. 1 against the pressure of spring 57 in the eventthat pressure develops within the chamber 55 because of a malfunctioningof the valves or for other reasons which are well understood by thoseskilled in the art. Valve 58 effects communication between chamber 55and a chamber 59 that connects to the sump 101 via line 102 in astandard manner, and it is to this sump that fluid will be directed inthe event of the movement of the relief valve 58 against the pressure ofthe spring 57.

Fluid flows normally through the passage 56, as already set forth, intothe cylindrical chamber 60 in which the valve spool 45 slides, and thenthrough a passage 62 toward the cylindrical chamber 65 in which thevalve spool 12 is adapted to slide. With the valve spool 12 in theposition shown in FIG. 1, the fluid will flow into the cylindricalchamber 65 and then through the valve port 66 toward the reverse clutch.Since the clutch is entirely standard, and may be of any type, it is notshown, except by the arrow 67.

In FIG. 3, the directional valve spool 12 is shown in its forwardposition, and if valve spool 45 were in its position of FIG. 1, fluidwould flow from the cylindrical chamber 65 through port 68 in thedirection of the arrow 69 to the forward clutch. If the valve 12 is in acentral or neutral position shown on FIG. 2, the port 66 and port 68will each be shut off by lands 70 and 71 of the valve spool 12, and theflow of fluid under pressure to both clutches will be prevented, so thatthe transmission will be in neutral.

When the valve spool 45 is in its position of FIG. 1, in which positionit is held by the pressure of the spring 47 against the piston rod 31,there will be full communication of fluid between the passage 56, thecylindrical chamber 60 and the passage 62, so that the positioning ofthe directional valve spool 12 in forward or reverse will mean thatthere will be full flow of fluid to the forward or reverse clutches. Letus assume now that the valve 12 is in forward drive position asillustrated in FIG. 3, and that it is desired to inch. In other words,it is the operators wish to have the engine operate at a relatively highspeed, but that the truck move forward at an exceedingly slow speed.

The driver, with the engine operating at relatively high speed, willmove the treadle 51 from its dash and dotted line position in FIG. 3 toits full line position. This will cause the rod 48 to move to itsposition of FIG. 3. During this movement, a part 72 of the valve 45 willgradually close communication between a port 73 of the chamber 60 and aport 74 of the said chamber. At the same time the tapered portion 75 ofthe valve spool 45 will move into a position to cause communicationbetween the chamber 60 and chamber 59, which, as will be remembered, isthe chamber communicating with the sump 101 in the event the pressurerelief valve 58 is actuated. It is obvious that when the part 72 of thespool 45 closes communication between the ports 73 and 74, fluid canonly flow into the chamber 60 through the small bypass passage in thespool 45, and relatively little fluid pressure is available to theclutches under the control of the directional valve 12. At the sametime, as seen in FIG. 3, communication is established between theforward clutch and the chamber 59 to the sump 101 via line 102, throughport 68, chamber 65, passage 62. chamber 60 and tapered surface 75 ofvalve body 45, so that pressure against the forward clutch is relieved.Of course, taper 75 is determined so that the control of the clutchesexercised by the spool 45 under the manual positioning of the inchingtreadle 51 is as the designer requires. Actually, as will beappreciated, when the valve spool 45 is in the extreme left positionshown in FIG. 3, the forward and reverse clutches should be relievedentirely of pressure. It is therefore possible to obtain effectiveinching through manipulation of the spool 45, as should now be ratherapparent.

I shall now describe just what happens when the valve spool 12 is in onedirectional position and is moved toward a neutral position preliminaryto being moved to a reverse directional position. In other words, Ishall indicate just what happens when an attempt is made to plug thevehicle by moving from one directional position to a reverse position.In this case, I shall describe what happens when an attempt is made tomove from a reverse directionalposition shown in FIG. 1 to a forwarddirectional position.

Fluid flows under the control of spool 45 and directional spool 12 tothe reverse clutch when the parts are positioned as in FIG. I, asalready set forth. Let us now assume that the operator wishes to reversethe drive and therefore moves the directional spool 12 first into itsneutral position of FIG. 2. When he does this, he places the passage 17and the opening 18 of valve 16 in a position in which the opening 18communicates with the port 20 of valve body A. Now, the opening 18,instead of being in communication with the atmosphere as in FIG. 1, isin communication with the manifold M through the pipe 25. Therefore, thevacuum at the manifold acts to unseat the valve 28 so that air ispartially exhausted from the cylinder 30 at the left of piston 32through the pipe 29. Therefore, the atmospheric pressure exerted throughthe opening 33 is applied against the piston 32 moving the piston 32into its position of FIG. 2. Now, the piston rod 31 has acted to movethe valve spool 45 to the left to its position of FIG. 2, in whichposition flow of fluid to the chamber 65 of the valve body issubstantially reduced and substantially no fluid pressure is directed tothe forward and reverse clutches.

Interestingly enough, because of the buildup of pressure within thevalve body 10 through flow from pump P, the relief valve 58 will move tothe left against the pressure of its spring 57 as seen in FIG. 2 so thatfluid flowing from the pump will move toward the sump 101 through thechamber 59.

Let us now assume that the operator continues the movement of theactuator valve 16, moving it together with the valve spool 12 to theforward position of FIG. 3. As a matter of fact, the operator mightconsider moving the actuator valve back to its position of FIG. I. Inthat event the apparatus would function in the same manner as thoughreversal were desired. Assuming that the actuator valve 16 is moved intothe position of FIG. 3, it will be seen that the opening 18 is now incommunication with the port 21, and therefore in communication with thechamber 22 and with the atmosphere through the screen 23. Air underatmospheric pressure is now allowed to flow through the screen 23, thechamber 22, and valve port 21, the opening 18, passage 17, the pipe 26,and toward the valve body 27. Because the ball valve 28 will be seatedas shown in FIG. 3, there will be no flow possible through the valvebody 27. Therefore, the air will be directed by the bypass pipe 35 underthe control of the valve 36, as set by the manually operated part 37.The air as metered by the valve 36, will move through the pipe 29 andinto the cylinder 30. With air thus introduced under atmosphericpressure into the cylinder 30, it is obvious that there will be agradual balancing of pressures at the two sides of the piston 32, sothat the spring 47 will be able to move the valve spool 45 from itsposition of FIG. 2 back toward its position of FIG. 1. This movement maybe as slow as required by conditions and is determined by the valve 36.Thus, it will take some little time for the pressure to be equalized sothat the piston 32 and its rod 31 may move from the position of FIG. 2to the position of FIG. 1 to allow the valve spool 45 to move also fromits position of FIG. 2 to its position of FIG. I, in which fullhydraulic pressure is applied against the clutches.

It will now be appreciated that when the directional valve spool I2 isin its reverse or forward drive position, the left hand side of piston32 in the cylinder 30 is always in communication with atmosphericpressure. However, when the valve spool 12 is in its central or neutralposition illustrated in FIG. 2, the cylinder at the left side of thepiston 32 is in communication with a source of vacuum. Therefore,whenever the directional valve spool 12 is moved from a directionalposition into a neutral position, the clutches are relieved of allpressure. Moreover, when the valve spool 12 is then moved into adirectional position, the flow of fluid tending to move the piston 32from the position of FIG. 2 to the position of of FIG. 1 will be meteredunder the control of the valve 36 so that the application of fluidpressure to the forward or rearward directional clutches will be gradualand the clutches will not be applied so as to allow the truck to jerkinto forward or reverse motion. As is also quite apparent, it isimpossible to move from either directional position except by going intoneutral position and placing the valve body 12 in neutral, at which timeboth clutches are relieved of fluid pressure and it is then necessaryfor the clutches to come under the control of the cylinder 30 and to bemoved gradually into a clutching relationship so that the change indirection will obviously be controlled. In other words, plugging controlis inherent in the invention.

It is further quite readily seen that through the simple provision of atreadle, it is possible for me to obtain inching control as I havealready described in detail, through movement of the valve spool 45 bythe treadle 51. This movement takes place exactly as under the controlof the piston rod 31 and the piston 32, but at a speed determined by theoperator.

In FIG. 4, I show a ball that coacts with any one of three depressions86, 87 and 88 of spool 12, to hold the spool 12 yieldingly in one of itsthree positions corresponding to forward, neutral or reverse. A spring880 holds the ball in position, the spring acting against a headed screw89, as is standard in the art.

In FIG. 5, I illustrate a modification of my invention, utilizing a partshown in FIG. 4. Thus, I substitute an electromagnet 90 for the variouspipes and the actuator valve 16 of my preferred form. Then, theelectromagnet 90 instead of engine vacuum is adapted to control thepiston rod 310 and piston 32a which are the same generally as piston rod31 in their action. Rod 31a traverses electromagnet 90 and functions asits armature. The valve spool 12, as shown in FIG. 4, is equipped with acontact portion 91, it being understood that the remainder of the valvesurrounding the contact 91 will naturally be formed of a suitableinsulating material 92. When the valve spool 12 is in its position ofFIG. 4, which is its neutral position illustrated in FIG. 2, contactwill be made between the contact portion 91 and a pair of wires 93 and93a running from the valve body 10 to the electromagnet 90. Obviously,therefore, whenever the valve spool 12 is in its neutral position, theelectromagnet 90 will be excited.

Cylinder 30a of the modification of FIG. 5 is similar to the cylinder 30of the first modification, except that it has a metered passage for theadmission of air, designated by reference numeral 94, and is equippedwith a ball valve that is normally seated against a passage 96, as isstandard in the art. When the electromagnet 90 is excited, by movementof valve 12 to neutral, the piston 32a is moved to the left to itsposition of FIG. 5, and air will be allowed to escape from the cylinder30a by the unseating of the ball valve 95. Obviously the piston rod 310will act as does the piston rod 31 in the first modification, and thevalve spool 45 will be moved to its position shown in FIG. 2. Now,should the valve spool 12 be placed in a forward or reverse driveposition, the circuit established at 91 through the electromagnet 90 bywires 93 and 931, will be broken, and the electromagnet 90 allows thepiston rod 31a to move to the right from its position of FIG. 5 underthe pressure of valve body 45 and its spring 47. The piston rod 310 andits piston 32a will now move to the right, allowing valve 45 to movealso, but rather slowly, under the control of the metering valve 94. Inother words, the metering valve 94 will act as does the valve 36,allowing a relatively slow application of hydraulic pressure to theforward and reverse clutches by permitting movement of the valve spool45 as described with regard to the first modification.

I believe that those skilled in the art will now understand my inventionrather clearly, and will appreciate its inherent merits.

I now claim:

l. A forward and reverse clutch system having a directional valvemovable between a neutral position, and forward and reverse directionalpositions in which directional positions it directs fluid to forward orreverse clutches of an engine driven transmission, a control valve tocontrol the fluid flowing to the forward and reverse clutches under thedirectional control of said directional valve, whereby to vary thepressure of fluid applied to said clutches, and vacuum actuated meansfor moving said control valve.

2. In the combination of claim 1, the feature that said vacuum isdeveloped by said engine and that atmospheric pressure moves saidcontrol valve as the degree of vacuum increases, in a direction todecrease the flow of fluid to said clutches.

3. In the combination of claim 1, the feature that the application ofsaid vacuum is controlled by movement of said directional valve.

4. In the combination of claim 3, the feature that the application ofsaid vacuum is effected by movement of said directional valve to aneutral position.

5. In the combination of claim 4, the feature that said directionalvalve must be moved to neutral in order to shift it from one directionalposition to another, so that said vacuum must be applied duringdirectional shifting.

6. In the combination of claim 5, the feature that the said vacuum willeffect the movement of the control valve to a degree that will causesubstantial release of the forward or reverse clutches.

7. In the combination of claim 2, the feature that an actuator valvemovable with said directional valve controls the application of vacuum.

8. In the combination of claim 7, the feature that said actuator valvein one position subjects the control valve to said vacuum and in anotherposition substitutes at least atmospher ic pressure for said vacuum inorder to move said control valve to increase fluid flow to saidclutches.

9. In the combination of claim 8, the feature that the said substitutionof at least atmospheric pressure is through a metering valve wherebysaid fluid flow will be increased gradually.

10. In the combination of claim 8, the feature that said actuator valveis moved coincidentally with said directional valve.

11. In the combination of claim 9, the feature that said actuator valveis moved coincidentally with said directional valve.

12. In the combination of claim I, the feature that said control valveis movable also by an inching member to vary the pressure of fluidapplied to said clutches.

13. In the combination of claim 6, the feature that said control valveis movable also by an inching treadle or the like whereby to effectdecrease of fluid flow to said clutches when said directional valve isin a forward and in a reverse directional position.

14. In the combination of claim I, the feature that a spring urges saidcontrol valve to a full flow position in which predetermined full flowof fluid to said clutches is effected, a piston or the like exposed atone side to atmospheric pressure pressing the piston against saidcontrol valve in a direction reverse to that in which it is urged by theforce of said spring, a passage leading to the other side of saidpiston, means connecting said passage to a vacuum source, and anactuator valve for controlling the application of vacuum through saidpassage.

15. In the combination of claim 14, the feature that there is a bypassbetween said vacuum source and said passage whereby atmospheric pressuremay be applied to both sides of said piston, and means whereby saidactuator valve controls said bypass.

16. In the combination of claim 15, the feature that said bypass ismetered so that atmospheric pressure therethrough is applied gradually.

17. In the combination of claim 16, the feature that said actuator valveis moved coincidentally with said directional valve and opens saidbypass when said directional valve is in neutral position.

18. In the combination of claim 14, the feature that said control valveis movable by an inching treadle against the force of said springwhereby to eflect decrease of fluid flow to said clutches when saiddirectional valve is in a forward and in a reverse directional position.

19. A forward and reverse clutch system having a directional valvemovable between a neutral position and forward and reverse directionalpositions in which directional positions it directs fluid to forward orreverse clutches of an engine driven transmission, and including acontrol valve to control the fluid flowing to the forward and reverseclutches under the control of the directional valve, whereby to vary thepressure of fluid applied to said clutches, the improvement thatcomprises operating means for moving said control valve in a directionto decrease the flow of fluid to said clutches whereby to effectslipping and substantial release of said clutches, and means wherebymovement of said control valve in a reverse direction to increase theflow of fluid to said clutches, after release of said control valve fromsaid operating means, is metered automatically so as to be gradual.

20. In the combination of claim 19, the feature that said operatingmeans for moving the control valve to decrease fluid flow are renderedeflective by movement of said directional valve to neutral position.

21. In the combination of claim I9, the feature that said operatingmeans are a cylinder with a piston in said cylinder exposed at one sideto atmospheric pressure and at the other side to pressure as determinedby a passage from said cylinder communicating alternately with theatmosphere via a metering valve or with a vacuum source.

22. In the combination of claim 21, the feature that means operatedcoincidentally with said directional valve control the communication ofsaid passage with the atmosphere and said vacuum source.

23. In the combination of claim 19, the feature that said control valveis movable also by an inching treadle or the like whereby to effectdecrease of fluid flow to said clutches.

24. A forward and reverse clutch system having a directional valvemovable between a neutral position, and forward and reverse directionalpositions, in which directional positions it directs fluid to forward orreverse clutches of an engine driven transmission, a control valve tocontrol the flow of fluid under pressure to said clutches, and meansactuated by movement of said directional valve for effecting movement ofsaid control valve to control flow of fluid toward said clutches.

25. In the combination of claim 24, the feature that movement of saiddirectional valve to neutral eflects relatively swift movement of saidcontrol valve to decrease fluid flow and consequent substantial releaseof said clutches, and means whereby movement thereafter of saiddirectional valve to a directional position effects relatively slowmovement of said control valve in a direction to effect relativelyslowly the increased application of fluid pressure to said clutches.

26. In the combination of claim 25, the feature that said control valveis movable also by an inching treadle or the like whereby to effectdecrease of fluid flow to said clutches when said directional valve isin a forward and in a reverse directional position.

27. In the combination of claim 25, the feature that an electromagnet isenergized by movement of said directional valve to neutral for movingsaid control valve to decrease fluid flow, and means for moving saidcontrol valve to increase flow when said electromagnet is deenergized.

28. In the combination of claim 27, the feature that said electromagnetis deenergized when said directional valve is moved to forward orreverse, and a dashpot or the like for controlling the movement of saidcontrol valve when it is released by deenergizing of said electromagnet.

29. In the combination of claim 19, the feature that said operatingmeans is an electromagnet, and means for energizing and deenergizingsaid electromagnet.

30. In the combination of claim 29, the feature that said electromagnetwhen dcenergized permits said control valve to that a spring

1. A forward and reverse clutch system having a directional valvemovable between a neutral position, and forward and reverse directionalpositions in which directional positions it directs fluid to forward orreverse clutches of an engine driven transmission, a control valve tocontrol the fluid flowing to the forward and reverse clutches under thedirectional control of said directional valve, whereby to vary thepressure of fluid applied to said clutches, and vacuum actuated meansfor moving said control valve.
 2. In the combination of claim 1, thefeature that said vacuum is developed by said engine and thatatmospheric pressure moves said control valve as the degree of vacuumincreases, in a direction to decrease the flow of fluid to saidclutches.
 3. In the combination of claim 1, the feature that theapplication of said vacuum is controlled by movement of said directionalvalve.
 4. In the combination of claim 3, the feature that theapplication of said vacuum is effected by movement of said directionalvalve to a neutral position.
 5. In the combination of claim 4, thefeature that said directional valve must be moved to neutral in order toshift it from one directional position to another, so that said vacuummust be applied during directional shifting.
 6. In the combination ofclaim 5, the feature that the said vacuum will effect the movement ofthe control valve to a degree that will cause substantial release of theforward or reverse clutches.
 7. In the combination of claim 2, thefeature that an actuator valve movable with said directional valvecontrols the application of vacuum.
 8. In the combination of claim 7,the feature that said actuator valve in one position subjects thecontrol valve to said vacuum and in another position substitutes atleast atmospheric pressure for said vacuum in order to move said controlvalve to increase fluid flow to said clutches.
 9. In the combination ofclaim 8, the feature that the said substitution of at least atmosphericpressure is through a metering valve whereby said fluid flow will beincreased gradually.
 10. In the combination of claim 8, the feature thatsaid actuator valve is moved coincidentally with said directional valve.11. In the combination of claim 9, the feature that said actuator valveis moved coincidentally with said directional valve.
 12. In thecombination of claim 1, the feature that said control valve is movablealso by an inching member to vary the pressure of fluid applied to saidclutches.
 13. In the combination of claim 6, the feature that saidcontrol valve is movable also by an inching treadle or the like wherebyto effect decrease of fluid flow to said clutches when said directionalvalve is in a forward and in a reverse directional position.
 14. In thecombination of claim l, the feature that a spring urges said controlvalve to a full flow position in which predetermined full flow of fluidto said clutches is effected, a piston or the like exposed at one sideto atmospheric pressure pressing the piston against said control valvein a direction reverse to that in which it is urged by the force of saidspring, a passage leading to the other side of said piston, meansconnecting said passage to a vacuum source, and an actuator valve forcontrolling the application of vacuum through said passage.
 15. In thecombination of claim 14, the feature that there is a bypass between saidvacuum source and said passage whereby atmospheric pressure may beapplied to both sides of said piston, and means whereby said actuatorvalve controls said bypass.
 16. In the combination of claim 15, thefeature that said bypass is metered so that atmospheric pressuretherethrough is applied gradually.
 17. In the combination of claim 16,the feature that said actuator valve is moved coincidentally with saiddirectional valve and opens said bypass when said directional valve isin neutral position.
 18. In the combination of claim 14, the featurethat said control valve is movable by an inching treadle against theforce of said spring whereby to effect decrease of fluid flow to saidclutches when said directional valve is in a forward and in a reversedirectional position.
 19. A forward and reverse clutch system having adirectional valve movable between a neutral position and forward andreverse directional positions in which directional positions it directsfluid to forward or reverse clutches of an engine driven transmission,and including a control valve to control the fluid flowing to theforward and reverse clutches under the control of the directional valve,whereby to vary the pressure of fluid applied to said clutches, theimprovement that comprises operating means for moving said control valvein a direction to decrease the flow of fluid to said clutches whereby toeffect slipping and substantial release of said clutches, and meanswhereby movement of said control valve in a reverse direction toincrease the flow of fluid to said clutches, after release of saidcontrol valve from said operating means, is metered automatically so asto be gradual.
 20. In the combination of claim 19, the feature that saidoperating means for moving the control valve to decrease fluid flow arerendered effeCtive by movement of said directional valve to neutralposition.
 21. In the combination of claim 19, the feature that saidoperating means are a cylinder with a piston in said cylinder exposed atone side to atmospheric pressure and at the other side to pressure asdetermined by a passage from said cylinder communicating alternatelywith the atmosphere via a metering valve or with a vacuum source.
 22. Inthe combination of claim 21, the feature that means operatedcoincidentally with said directional valve control the communication ofsaid passage with the atmosphere and said vacuum source.
 23. In thecombination of claim 19, the feature that said control valve is movablealso by an inching treadle or the like whereby to effect decrease offluid flow to said clutches.
 24. A forward and reverse clutch systemhaving a directional valve movable between a neutral position, andforward and reverse directional positions, in which directionalpositions it directs fluid to forward or reverse clutches of an enginedriven transmission, a control valve to control the flow of fluid underpressure to said clutches, and means actuated by movement of saiddirectional valve for effecting movement of said control valve tocontrol flow of fluid toward said clutches.
 25. In the combination ofclaim 24, the feature that movement of said directional valve to neutraleffects relatively swift movement of said control valve to decreasefluid flow and consequent substantial release of said clutches, andmeans whereby movement thereafter of said directional valve to adirectional position effects relatively slow movement of said controlvalve in a direction to effect relatively slowly the increasedapplication of fluid pressure to said clutches.
 26. In the combinationof claim 25, the feature that said control valve is movable also by aninching treadle or the like whereby to effect decrease of fluid flow tosaid clutches when said directional valve is in a forward and in areverse directional position.
 27. In the combination of claim 25, thefeature that an electromagnet is energized by movement of saiddirectional valve to neutral for moving said control valve to decreasefluid flow, and means for moving said control valve to increase flowwhen said electromagnet is deenergized.
 28. In the combination of claim27, the feature that said electromagnet is deenergized when saiddirectional valve is moved to forward or reverse, and a dashpot or thelike for controlling the movement of said control valve when it isreleased by deenergizing of said electromagnet.
 29. In the combinationof claim 19, the feature that said operating means is an electromagnet,and means for energizing and deenergizing said electromagnet.
 30. In thecombination of claim 29, the feature that said electromagnet whendeenergized permits said control valve to move to permit full flow offluid to said clutches, and a dashpot to slow down said movement.
 31. Inthe combination of claim 30, the feature that a spring propels saidcontrol valve to full flow position.